Preparation of aliphatic olefins from saturated hydrocarbons

ABSTRACT

A PROCESS FOR CONVERTING SATURATED HYDROCARBONS TO ALIPHATIC OR ALICYCLIC OLEFINS HAVING THE SAME NUMBER OF CARBON ATOMS AS THE FEED IS DESCRIBED. THE FEED CAN BE C4-C10 N-PARAFFINS, CERTAIN C4-C10 ISOPARAFFINS, CYCLOHEXANE OR METHYL-SUBSTITUTED CYCLOHEXANES OF THE C7-C10 RANGE. THE OLEFIN PRODUCT FROM N-PARAFFIN FEED IS SINGLY BRANCHED OLEFIN. THE PROCESS INVOLVES RREACTING THE SATURATED HYDROCARBON WITH A C10-C13 ADAMANTANE HYDROCARBON IN THE PRESENCE OF STRONG SULFURIC ACID TO FORM A HIGHER ALKYLATED ADAMANTANE, FOLLOWED BY CRACKING OF THE LATTER TO YIELD THE OLEFIN AND RE-FORM THE C10-C13 ADAMANTANE HYDROCARBON. THE LATTER CAN BE RECYLED. THE PROCEDURE IS ALSO APPLICABLE TO THE RECOVERY OF OLEFINS FROM SPENT SULFURIC ACID PREVIOUSLY USED IN THE TREATMENT OF OLEFINIC STOCKS, E.G. IN AN OLEFIN-ISOPARAFFIN ALKYLATION PROCESS

Dec. 26, 1972 DMA DMA RECYCLE MAKE-UP I l4 I3 R; E. MOORE PREPARATION OF ALIPHATIC OLEFINS FROM SATURATED HYDROCARBONS Filed May 26,

'q-BUTANE FEED ALKYLATION STRONG SULFURIC SETTLING DISTILLATION 25 HIGH BOILING l I-BUTANE RECYCLE ALKYLATED DMA ALKYLATION PRODUCT CRACKING DISTILLATION Tb ISOBUTENE INVENTOR ROBERT E. MOORE ,BYUZ-H ATTORNEY United States Patent 3,707,576 PREPARATION OF ALIPHATIC OLEFINS FROM SATURATED HYDROCARBONS Robert E. Moore, Wilmington, Del., assignor to Sun Research and Development Co., Philadelphia, Pa. Continuation-impart of applications Ser. No. 80,779, Oct. 14, 1970, and Ser. No. 91,183, Nov. 19, 1970. This application May 26, 1971, Ser. No. 147,011

Int. Cl. C07c 3/54, 13/28 U.S. Cl. 260666 A 16 Claims ABSTRACT OF THE DISCLOSURE A process for converting saturated hydrocarbons to aliphatic or alicyclic olefins having the same number of carbon atoms as the feed is described. The feed can be C -C n-parafiins, certain C -C isoparaffins, cyclohexane or methyl-substituted cyclohexanes of the C -C range. The olefin product from n-parafiin feed is singly branched olefin. The process involves reacting the saturated hydrocarbon with a C -C adamantane hydrocarbon in the presence of strong sulfuric acid to form a higher alkylated adamantane, followed by cracking of the latter to yield the olefin and re-form the C -C adamantane hydrocarbon. The latter can be recycled. The procedure is also applicable to the recovery of olefins from spent sulfuric acid previously used in the treatment of olefinic stocks, e.g. in an olefin-isoparaffin alkylation process.

CROSS REFERENCES TO RELATED APPLICATIONS My copending application Ser. No. 80,779, filed Oct. 14, 1970, of which this application is a continuation-in-part, now U.S. Pat. No. 3,646,233 issued Feb. 29, 1972, discloses the reaction of adamantane hydrocarbons with nparatfins or isoparafiins in the presence of strong sulfuric acid to yield two types of alkylation products: (1) alkylated adamantane in which the single adamantane nucleus contains an additional alkyl group derived from the nparaflin or isoparafiin; and (2) bis-type product having two adamantane nuclei linked through an alkylene moiety derived from the n-paraffin or isoparaflin.

My copending application Ser. No. 91,183, filed Nov. 19, 1970, also of which this application is a continuationin part, now U.S. Pat. No. 3,646,234 issued Feb. 29, 1972, describes an analogous alkylation of adamantane hydrocarbons by means of sulfuric acid, using naphthenes instead Of paraflins as the other reactant. This reaction likewise can give two types of alkylation products analogous to those mentioned above.

BACKGROUND OF THE INVENTION This invention relates to the preparation of aliphatic or alicyclic olefins from saturated hydrocarbons by a novel process involving alkylation and dealkylation of adamantane nuclei.

The adamantane nucleus has ten carbon atoms, four of which are bridgehead carbons as can be seen from the following typographical representation:

Patented Dec. 26, 1972 As shown, the bridgehead carbon atoms customarily are designated by the numerals 1, 3, 5 and 7 respectively, and these bridgehead positions are all equivalent to each other in the nuclear structure.

Adamantane hydrocarbons useful in the present process are of the C C range and include adamantane, methyladamantanes, dimethyladamantanes and trimethyladamantanes, with the methyl substituents being at either bridgehead or non-bridgehead positions or both. Methods of preparing these hydrocarbons are well known in the art; see, for example, the following U.S. patents: Schneider 3,128,316, dated Apr. 7, 1964; Schneider et a1. 3,336,406, dated Aug. 15, 1967; Schneider 3,356,751, dated Dec. 5, 1967; Hala et al. 3,418,387, dated Dec. 24, 1968; and Capaldi et a1. 3,489,817, dated Ian. 13, 1970.

The preparation of olefins from saturated hydrocarbons heretofore usually has involved cracking of the saturated feed to produce olefins having less carbon atoms per molecule or catalytic dehydrogenation of the saturated feed to give olefins with the same number of carbon atoms. In the case of naphthenes having a cyclohexyl ring, the latter procedure generally is not suitable for making the corresponding olefin since the cyclohexyl ring has a strong tendency to dehydrogenate to a benzenoid ring.

SUMMARY OF THE INVENTION The present invention provides a means of converting saturated hydrocarbons of certain classes to aliphatic or alicyclic olefins having the same number of carbon atoms per molecule as the feed. The invention is applicable to the following feed hydrocarbons: (1) C -C3 n-parafiins, which convert to singly branched monoolefins; (2) C -C singly branched isoparafiins and C doubly branched isoparaflins, which convert to branched monoolefins having the same number of carbon atoms as the feed; and (3) C -C naphthenes having a cyclohexyl ring and 0-4 methyl substituents, which convert to cyclic monoolefins mainly having C rings but also having C rings. In each case the conversion is effected by first reacting the saturated feed hydrocarbon with adamantane (C or methylsubstituted adamantanes (C -C in the presence of strong sulfuric acid to alkylate the nucleus at a bridgehead position. The resulting alkylated adamantane is then subjected to cracking conditions which break the new alkyl or cycloalkyl group from the nucleus, thus giving an olefin while re-forming th starting adamantane hydrocarbon which can be recovered and recycled.

The process according to the invention comprises the following steps:

(A) contacting a mixture consisting essentially of (1) sulfuric acid having a strength of 105% (2) adamantane hydrocarbon of the C -C range having 0-3 methyl groups as the only substituents on the adamantane nucleus,

(3) and saturated hydrocarbon of the group (a) C C n-paraflins,

(b) C C isoparaffins selected from isobutane,

isopentane, singly and doubly branched isohexanes and singly branched 07-010 isoparafiins,

(c) and C C naphthenes having a cyclohexyl ring and 0-4 methyl groups as the only substituents thereon,

at an alkylating temperature above the freezing point of said acid but below C., whereby an additional substituent derived from and having the same number of carbon atoms as said saturated hydrocarbon becomes attached to the adamantane nucleus;

(B) Separating the resulting alkylated adamantane;

(C) cracking said alkylated adamantane to sever said additional substituent from the adamantane nucleus; (D) and recovering a product comprising olefin having the same number of carbon atoms as said add tional substituent.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a schematic fiowsheet illustrating the steps of the process, using dimethyladamantane (designated as DMA) as the adamantane hydrocarbon and n-butane as the feed, the latter being converted to isobutene as the olefinic product.

DESCRIPTION One embodiment of the invention comprises the conversion of normal parafiins of the C C range, more preferably of the C -C range, to singly branched aliphatic olefins. The olefin will have the same number of carbon atoms as the n-parafiin feed. Examples of this are conversion of n-butane to isobutene (described hereinafter in conjunction with the drawing), the conversion of n-pentane to isopentenes and the conversion of nhexane to isohexenes. Other examples are the preparation of singly branched isooctenes from n-octane or singly branched isodecenes from n-decane.

Isoparafiins of the C C range which are singly branched, or hexanes which are doubly branched can be used in the process instead of straight chain parafiins to give branched olefins having the same number of carbon atoms as the isoparaffin feed. The isoparafiin used in this embodiment preferably is of the C -C range. Specific examples are the conversion of isobutane to isobutene and the preparation of isopentenes from isopentane.

In a further embodiment of the invention, the feed can be cyclohexane or methyl-substituted cyclohexanes with 1-4 methyl groups which can be located at any positions on the cyclohexyl ring. In the process these are converted to cyclic monoolefins having the same number of carbon atoms as the naphthene feed. These cyclic olefins mainly have C rings but also usually contain methyl-substituted cyclopentenes. As previolsly pointed out, the conversion of C -ring naphthenes to cyclic monoolefins generally cannot be successfully achieved by catalytic dehydrogenation since the ring strongly tends to dehydrogenate further, giving aromatic hydrocarbon products.

The other reactant in all of the foregoing embodiments can be any C -C adamantane hydrocarbon having 3 methyl groups as the only substituents on the adamantane nucleus. The methyl group or groups can be located at bridgehead or non-bridgehead positions or both. Some examples of this reactant are as follows: adamantane; 1- methyladamantane; Z-methyladamantane; 1,2-, 1,3- and 1,4-dimethyladamantane; and 1,2,4-, 1,2,5-, 1,3,4- and 1, 3,6 trimethyladamantane. Preferably methyl-substituted adamantanes which are normally liquid at the temperature at which the alkylation step is operated are used in the process, rather than the normally solid materials such as adamantane and 1 methyladamantane. The dimethyladamantanes are most preferred as the adamantane hydrocarbon reactant.

Reaction of the adamantane hydrocarbon with the saturated hydrocarbon in accordance with the invention is effected by contacting a mixture of these reactants with strong sulfuric acid. The molar ratio of saturated hydrocarbon to the adamantane compound can vary in the reaction mixture but preferably should be at least 1:1 and more preferably in the range of 2:1 to :1. The ratio of acid to reactants can vary widely. Generally a volume excess of the acid relative to the reactants should be used and a volume ratio thereof in the range of 1:1 to 20:1 typically is employed. The mixture normally is an emulsion of acid and hydrocarbon phases, and the reaction takes place in the acid phase. The sulfuric acid should have a strength in the range of -105 H 80 equivalent by weight and more preferably above 94%, with strengths in the range of 96102% H 80 generally being most preferable. The reaction temperature can be from just above the freezing point of the acid used to about 100 C. and usually is in the range of 1075 C. When a lower alkane such as butane or isobutane is used as reactant, the reaction is conducted under suflicient pressure to maintain a substantial concentration of the alkane in the liquid phase.

Contact of the acid with the feed materials causes them to react in an unexpected manner, whereby the saturated hydrocarbon becomes an alkylating agent for the adamantane nucleus. The rate of reaction will depend upon the reaction temperature selected and the strength of the acid maintained in the reactor. The adamantane hydrocarbon slowly diffuses into the acid phase as the mixture is agitated, becoming solubilized therein probably at least mainly in the carbonium ion form. The saturated hydrocarbon reactant also diffuses from the hydrocarbon phase into the acid phase in order to react and the rate that this occurs depends on the degree of agitation, the temperature and the molecular weight of the parafiin used. The alkylated adamantane products precipitate from the acid phase as they are formed and become constituents of the hydrocarbon phase.

During the reaction the oxidizing power of the strong acid employed results in the conversion of hydrogen atoms derived from hydrocarbon reactant material into water. Concurrently sulfur dioxide is formed from the acid and tends to vaporize from the mixture unless the reaction is carried out under pressure. When the strength of the acid is high (e.g. l02-105% H 50 the reaction may occur so rapidly that the fast evolution of sulfur dioxide can present control problems unless the system is maintained under sufiicient pressure. As Water and sulfur dioxide are being formed, the strength of the sulfuric acid in the reaction mixtures tends to decrease. This can be compensated for by adding sulfur trioxide in amount to maintain the desired strength of acid in the system.

Following the alkylation step, separation of the acid phase from the hydrocarbon phase is effected by settling the mixture, and the hydrocarbon phase is then distilled to remove any unreacted feed materials, the latter being recycled for reuse. The desired product of the reaction is alkylated adamantane hydrocarbon having one nucleus per molecule and one more substituent thereon than was originally present. However there is usually also formed some amount of higher boiling alkylation product, referred to herein as bis-type product, having two adamantane nuclei per molecule linked through an alkylene or cycloalkylene radical. The additional substituent of the desired alkylation product as well as the alkylene or cycloalkylene radical of this bis-type product are both derived from the saturated hydrocarbon feed reactant and each has the same number of carbon atoms as the parafiin or naphthene employed. The mixture of products generally obtained is distilled to separately recover each of the two types of alkylation products formed in the reaction. The desired alkylated adamantane product is thereafter subjected to a cracking operation as hereinafter described.

As a specific illustration of the alkylation step of the present process, the reaction of n-pentane with 1,3-dimethyladamantane (DMA) is considered. This reaction is effected, for example, by contacting a mixture of DMA and n-pentane in a molar ratio of 1:3 with sulfuric acid having a strength of 100% H 80 at 50 C. for 10 hours. The acid and hydrocarbon layers are separated, the hydrocarbon layer is Washed with water or aqueous alkali to remove residual acid, and the hydrocarbon material is then fractionally distilled to recover the products. The alkyladamantane product upon analysis is found to be composed mainly of the following (hydrogen atoms omitted for convenience):

Specifically this product is 1,3-dimethyl-5-(3-methylbutyl)adamantane. Smaller amounts of isomeric product with the methyl branch in the C alkyl substituent positioned closer to the adamantane nucleus may also be produced, but the predominant isomer formed is the one shown. N isomer having an n-pentyl group is detected. A higher boiling bis-type product is also obtained and the major part thereof is found to correspond to the following structure:

This compound specifically is 1,4-bis(3,5-dimethyladamantyl-l-)-4-methylbutane. A minor amount of product which boils closely to this compound and appears to be isomeric thereto generally is also produced. The reaction may also produce small amounts of other products due to disproportionation and other reactions that may occur to minor extent.

The formation of bis-type product in the alkylation step can be minimized by utilizing in the reaction mixture 21 high ratio of the paraflin or cycloparaffin to adamantane hydrocarbon reactant, e.g. 3:1 or higher. However, in some cases it may be desirable to operate the process to obtain substantial yields of both types of alkylated products, inasmuch as the bis-type products are oils having good traction coefiicients and constitute an excellent component for incorporation in traction fluids. Consequently, it may be desirable to practice the process to convert the specified parafiins or naphthenes to monoolefins while simultaneously producing a heavy alkylation product for use in manufacture of traction fluid compositions.

It is characteristic of the alkylation products of the present alkylation step, when the feed is any of the nparatfins specified, that the alkyl and alkylene groups derived from the n-paraflin will have a single methyl branch. Furthermore the methyl substituent in the alkyl group will be attached mainly or at least to substantial extent to the second carbon adjacent the unattached end of the chain, while that in the alkylene group will be attached mainly or at least to substantial extent to an alpha carbon atom in the chain. In other words, for any of the C -C n-paraffin reactants, the alkyl and alkylene groups will conform, respectively, to the following arrangements:

(5H3 i "ca. w ir.-

naphthene as the alkylating agent, the reaction of cyclohexane with 1,3-dimethyladamantane (DMA) is considered. This reaction is effected, for example, by contacting a mixture of DMA and cyclohexane in a molar ratio of 1:4 with sulfuric acid having a strength of 100% H at 50 C. for 10 hours. The acid and hydrocarbon layers are separated, the hydrocarbon layer is washed with water or aqueous alkali to remove residual acid, and the hydrocarbon material is then fractionally distilled to recover the products. The alkyladamantane product upon analysis is found to be composed mainly of the following (hydrogen atoms omitted for convenience):

As indicated by the dangling valence, this is a mixture of isomers of bis(3,5 dimethyladamantyl-l)-cyclohexane. Formation of this bis-type product tends to be suppressed by increasing the ratio of cyclohexane to DMA in the reaction mixture.

The alkylation product containing one adamantane nucleus to which is attached the additional alkyl or cycloalkyl substituent serves as the precursor for the desired olefin product. The olefin is obtained by subjecting this alkylated adamantane to cracking conditions which sever the additional substituent from the nucleus without substantially cracking the nucleus or removing the methyl groups therefrom. This can be done by vapor phase cracking of the alkylated adamantane at a temperature in the range of 300-450 C. utilizing an acidic cracking catalyst. Any of the known or conventional cracking catalysts can be used for this purpose, such as silica-alumina, silicazirconia, acid-treated clays, fluorine-promoted aluminas and zeolitic cracking catalysts of the faujasite type. Any pressure can be used at which the alkylated adamantane will be in vapor form at the cracking temperature selected. Liquid hourly space velocities (LHSV) can vary widely, for example, being in the range of 0.1 to 10 vol./vo1. of catalyst/hr. If desired, the alkylated adamantane feed to the cracking step can be diluted with an inert hydrocarbon, such as benzene, which is thereafter separately recovered and recycled;

The reaction which occurs when the additional substituent is cracked from the adamantane nucleus can be illustrated by -the following equation wherein the alkylate is cyclohexyldimethyladamantane, which is the main alkylation product when cyclohexane is the feed:

(cracking conditions) Q In this case it can be seen that the overall process of alkylation followed by cracking in effect dehydrogenates the cyclohexane feed to cyclohexene, with dimethyladamantane being recovered for reuse. The hydrogen removed from the naphthene feed has reacted with the sulfuric acid during the alkylation step, causing a decrease in the acid strength.

As another illustration, the alkylation product obtained when n-butane is feed reactant undergoes cracking as (cracking conditions) In effect, the overall process in this case has both isomerized and dehydrogenated n-butane to yield isobutene. Again the removed hydrogen has reacted with the sulfuric acid in the alkylation step, resulting in a reduction of acid strength.

In the last illustration, a single olefin product is obtained from the process. However, when parafiins above C are used, a plurality of olefin isomers generally are produced due to isomerization of the double bond in the presence of the acidic cracking catalyst. Thus the olefin product in the case of n-pentane as feed is a mixture of isopentenes, while the olefin product when n-hexane is used comprises mixed isohexenes. When cyclohexane is the alkylating agent, a plurality of cyclic olefins generally are obtained from cracking step due to partial contraction of cyclohexyl to cyclopentyl rings during the alkylation step. This contraction also occurs to some extent when methyl-substituted cyclohexanes are used.

The accompanying drawing illustrates the invention in the form of a continuous process utilizing n-butane and dirnethyladamantane (DMA) as reactants. The n-butane is fed as a liquid under pressure alkylation step through line 11, while DMA is recycled to this step through lines 12 and 13. Makeup DMA is added to the system as needed via line 14. Strong sulfuric acid having a strength of, for example, 98% H 50 is fed to the alkylator through line 15. The molar ratio of n-butane to DMA in the hydrocarbon phase in alkylation zone 10 is maintained above 1:1 and preferably considerably above this proportion (e.g. 2:1 to 6: 1) whenever it is desirable that formation of the bis-type alkylation product be held to a low level. Means (not shown) are provided in the alkylation zone for intimately contacting the acid and hydrocarbon phases so that the mixture is kept emulsified. The temperature is maintained at any suitable level between the freezing point of the acid and 100 C., for example, in the range of 25-60 C. The residence time in alkylation zone 10 will vary depending upon such factors as the temperature selected, strength of acid used and degree of agitation, but generally will be in the range of 0.1 to 10 hours.

The emulsion is continuously withdrawn from the alkylation zone and passed through line 16 to pressure settler 17 where the phases stratify. The acid phase is removed via line 18 and recycled through line to alkylation zone 10. In order to maintain the strength of the acid, sulfur trioxide is added to it, as indicated by line 19, as needed to keep the strength of the acid at the desired level. Since continued reuse of the acid tends to cause the accumulation of organic components therein, such as adamantyl ketones and soluble tars, means indicated by dashed line 20 are provided for removing the acid phase intermittently or as a drag stream.

The hydrocarbon layer in settler 17 generally comprises excess n-butane, the desired alkylation product and bistype alkylation product which is higher boiling. It may also and often does contain a substantial amount of unreacted DMA which should be recovered for reuse. The mixture is sent through line 21 to distillation zone or zones 22 for separation of these components. As indicated, excess n-butane is recovered and recycled through line 23 back to the alkylation zone. The desired alkylated DMA is separated as a fraction through line 24 while the bis-type higher boiling alkylation product is obtained as bottoms via line 25. In case the reaction mixture fed to distillation zone 22 contains a substantial proportion of unreacted DMA, this component may be taken off as a separate cut and recycled, as indicated by dashed line 26, to line 12 for return to the alkylation zone. On the other hand, when the mixture contains a relatively small amount of unreacted DMA, this component can be taken off as a part of the alkylated DMA fraction in line 24 since it will not adversely affect the subsequent cracking step.

The bis-type alkylation product from line 25 has the same kind of structure as shown above for the case of n-pentane as feed reactant. It is generally a mixture of isomers of which the main component is 1,3-bis(3,S-di methyladamantyl-l )-3-methylpropane. This material is an oil having good traction coeflicient and is an excellent component of friction of traction fluid compositions. For a discussion of this type of lubricant, see F. G. Rounds, J. of Chem. and Eng. Data, vol. 5, No. 4, pp. 499-507 (October 1960).

The lower boiling alkylation product in line 24, which optionally may also include any unreacted DMA, is mainly 1,3-dimethyl 5 (Z-methylpropyl)adamantane. This material is sent to a cracking zone 27 and therein subjected to vapor phase cracking under conditions as previously described. This severs the iso-butyl group from the adamantane nucleus, in the manner shown in the last preceding equation, without substantially affecting the methyl groups on the nucleus. The result is that isobutene is produced and DMA is re-fonmed. The cracked mixture is sent through line 28 to another distillation zone 29 from which iso-butene is recovered through line 30. The re-formed DMA is withdrawn from the bottom of zone 29 and recycled via lines 12 and 13 back to alkylation zone 10.

When other C -C adamantane hydrocarbons and other paraffins or naphthenes are substituted, respectively, for DMA and n-butane, the process is operated in substantially the same manner as above-described. However, the olefinic product is usually a mixture of isomers in such other cases, being a single isomer only in the case of n-butane.

The specific examples set forth below illustrate results obtained under certain conditions for the alkylation step and for the cracking step.

EXAMPLES 1-5 In each of these five runs the reactants were n-hexane and 1,3-dimethyladamantane (DMA) and 25 ml. of strong sulfuric acid (100% H were used. The procedure was as follows. The acid at the desired temperature in a flask was stirred by means of a magnetic stirrer, the DMA was added in amount of about 2.3 g. (0.0139 mole) and 1.2 g. (0.0139 mole) of n-hexane was added, resulting in a molar ratio of DMA to n-hexane of 1:1. At selected times 1 ml. portions of the reaction mixture were taken, and the hydrocarbon phase was separated in each case and analyzed by GLC, with identification of components being done by IR, NMR and mass spectroscopy. The resuits of this set of runs along with various run conditions are shown in Table I. The product compositions given do not include any unreacted n-hexane and are based on materials boiling above this reactant.

When singly or doubly branched C isoparafiins, including 2- or 3-methylpentane, neohexane and 2,3-dimethylbutane, are substituted for n-hexane in the foregoing example, the alkylation reaction proceeds in sub TABLE I Reaction of n-hexane with dimethyladamantane Acid Product composition, percent strength, DMA/ percent 'Iemp., Time, Bis-type Run No n-Ce H2804 hrs. DMA C -DMA product The data in Table I show that DMA tends to react slowly at the relatively low temperatures used, giving both types of alkylation products with the bis type being formed in minor proportion. The structures of the C DMA product and the bis-type product were identified by IR, NMR and mass spectroscopy as mainly the following isomers, respectively:

The left-hand compound had a boiling point of about 309 C. at 760 mm. Hg absolute. The C -DMA product also included minor amounts of several isomer-s of this compound. The bis-type product was considerably higher boiling and was found to have a good traction coefficient, viz 0.061 by the Rounds procedure at 600 ft./min. bearing speed, as compared with values in the range of 0.03 to 0.05 exhibited by most hydrocarbons in this test.

The products from any of Runs 1-5 preferably would be fractionated to remove DMA as well as the bis-type alkylate before the C -DMA is subjected to cracking in view of the large proportion of unreacted DMA in the alkylation product.

EXAMPLE 6 Alkylation of DMA with n-hexane One liter of sulfuric acid (100% H 50 was added to a reactor provided with a stirrer and was chilled to about 10 C. DMA in amount of 90 g. (0.55 mole) and nhexane in amount of 49.4 g. (0.57 mole) were added and the mixture was stirred vigorously for 8 hours. After addition of the reactants, the temperature was allowed to rise and most of the reaction occurred at about room temperature. The reaction mixture was then extracted several times with n-pentane, and the combined extract layer was partially evaporated to remove about 75% of the solvent. The residue was passed through a column of alumina, and the efiluent therefrom was then distilled to remove the rest of the pentane and to separately obtain the reaction products. Products obtained mainly were 23.9 g. of C -DMA and 16.2 g. of bis-type product. The yield of C -DMA based on DMA charged was about 18%.

stantially the same fashion although differences in reaction rates and product compositions are noted.

EXAMPLE 7 Alkylation of DMA with n-pentane Another run was made in a manner similar to Example 6, using one liter of H SO 100 g. (0.61 mole) of DMA and 47 g. (0.65 mole) of n-pentane. The mixture was reacted for a total of 5 hours, following which the same recovery procedure was used as described for Example 6. Products obtained mainly were 16.7 g. of C DMA and 7.5 g. of the bis-type product. The C -DMA was found to be analogous to the main isomer of 0.;- DMA product of Table I, being essentially the single isomer, 1(3,5 dimethyladamantyl-l) 3 methylbutane. 'It had a boiling point of about 287 C. at 760 mm. Hg absolute.

EXAMPLE 8 Alkylation of DMA with n-heptane This run was made in similar fashion to the preceding run, using one liter of 100% H 50 100 g. (0.61 mole) of DMA and 61.5 g. (0.61 mole) of n-heptane. The reaction was carried out for 5 hours and the product recovery was done in the same manner. Products obtained mainly were 18.0 g. of C -DMA which had a boiling point of about 330 C. at 760 mm. Hg absolute and 12.0 g. of the bis-type product. Analysis showed that the C-; group in the main isomer of the C -DMA had the structure 0 -o--0-c-0-d-O and the alkylene group in the bis-type product was largely o -o-o-o-o-o--c- EXAMPLE 9 Alkylation of DMA with n-octane This run was made in the same manner as the preceding run, using one liter of 100% H 50 100 g. (0.61 mole) of DMA and 70.2 g. (0.61 mole) of n-octane. The reaction was carried out for a total of 5 hours. The product was composed mainly of 16.0 g. of Cg-DMA. and 11.6 g. of the bis-type product. The structures of these products were homologous to those of the corresponding products of Example 8 with one more methylene unit in the alkyl or alkylene chain.

EXAMPLE 10 Alkylation of DMA with 3-methylheptane Another run was made in substantially the same manner as Example 9 except that 3-methylheptane was substituted 11 in place of n-octane. The reaction proceeds somewhat faster in this case and gives products which are largely the same as those of the preceding example.

EXAMPLE 11 Alkylation of DMA with cyclohexane Another run made under substantially the same conditions as in Example 9 except that cyclohexane is substituted for n-octane in amount giving a 1:1, molar ratio of DMA to cyclohexane gives a hydrocarbon product layer having a composition by GLC analysis approximately as follows on a cyclohexane-free basis:

Percent Unreacted DMA 85 Methylcyclopentyl DMA 6 Cyclohexyl DMA 7 Bis-type product 2 These results show that some amount of isomerization of the C ring occurs in the reaction, so that methylcyclopentyl as well as cyclohexyl substituents on the adamantane nucleus are present in the alkylated product. Cracking of this alkylate thus yield both cycloh'exene and methylcyclopentenes.

When adamantane or other alkyladamantanes as herein defined are substituted for the DMA used in the foregoing examples, analogous results are obtained. Likewise when other C -C n-paraflins are substituted for the saturated hydrocarbon reactants employed in the examples above, analogous alkylation products are obtained.

Substantially equivalent results are also obtained in the alkylation step when weaker sulfuric acid as well as stronger acid up to 105% H 50 is used in place of the acid employed in the foregoing examples, although the rates of reaction vary accordingly. When the acid strength exceeds 102% H 80 the reaction has a tendency to proceed so fast that it may become uncontrollable at atmospheric pressure due to the rapid evolution of S Hence, in such case it is desirable to carry out the reaction in a closed system under pressure or at a relatively low temperature within the specified range.

EXAMPLE 12 The C -DMA prepared as described in Example 7 was subjected to cracking conditions using a commercial silicaalumina cracking catalyst. A feed mixture of 2 vols. of C -DMA and 8 vols. of benzene as inert diluent was vaporized and passed thuough a column containing the catalyst at a temperature of 380 C. The space rate (LHSV) was 1.0 based on the mixture or 0.2 based on the C -DMA. Under these conditions 40% of the C DMA cracked, giving DMA and isopentene. Analysis indicated that the isopentene fraction was composed of about 19% 3-methylpentene-I and 81% 2-methylpentene-2.

EXAMPLE 13 Another sample of C -DMA was cracked under the same conditions as in the preceding example except that the LHSV was increased to 2.0 based on the feed mixture or 0.4 based on the C -DMA. In this case 25% of the C -DMA cracked, giving the same products as before.

EXAMPLE 14 Percent Peak 1 11 Peak 2 37 Peak 3 52 The chromatograph indicated that peak 3 contained at least three isohexene isomers. Thus cracking of the C DMA gave an olefin product composed of at least five isohexenes.

The cracking conditions described in Examples 12-14 should not be considered as representing optimum conditions for cracking the alkylated adamantane products. In any case the uucracked alkylated adamantane material can be separated from the cracked products by distillation and recycled to the cracking zone for further conversion.

In another aspect the invention also provides a way of recovering olefinic hydrocarbon from sulfuric acid which has been used as catalyst in another process, such as in olefin-paraflin alkylation or olefin polymerization. Such other process characteristically involves contacting a hydrocarbon feed containing olefinic hydrocarbon having at least three carbon atoms per molecule with the liquid catalyst as a separate phase under conditions causing the formation of aliphatic ester of sulfuric acid Which remains in the catalyst phase, whereby the catalyst eventually becomes spent. The term spent as used herein means that the strength of the acid has dropped below the level desired in the process and not necessarily that all catalyst activity has been lost. The procedure of the present invention can thereafter be used to recover olefins from the ester components of the spent catalyst. If the strength of the catalyst is above 90% H equivalent, then the catalyst can be treated directly with C -C adamantane as herein described. On the other hand, if the strength is below an H 80 content above this level first should be established by adding stronger sulfuric acid or preferably S0 The procedure for obtaining the olefins then involves the following steps:

( 1) contacting the catalyst phase with adamantane hydrocarbon of the C -C range having 0-3 methyl substituents on the adamantane nucleus at an alkylating temperature in the range of 10-100" C., whereby an additional alkyl group derived from said aliphatic ester becomes attached to the adamantane nucleus;

(2) separating the resulting alkylated adamantane;

(3) cracking the alkylated adamantane to sever the additional alkyl group from the adamantane nucleus;

(4 and then recovering olefinic hydrocarbon from the cracking reaction product.

These steps can be carried out under the same conditions as previously described for effecting the alkylation and cracking reactions.

The invention claimed is:

1. A process of preparing aliphatic or alicyclic olefins from saturated hydrocarbons which'comprises:

(A) contacting a mixture consisting essentially of (1) sulfuric acid having a strength of 90105% H2SO4,

(2) adamantane hydrocarbon of the C -C range having 0-3 methyl groups as the only substituents on the adamantane nucleus,

(3) and saturated hydrocarbon of the group (b) C -C isoparaffins selected from isobutane, isopentane, singly and doubly branched isohexanes and singly branched C -C isoparafiins,

(c) and C -C naphthenes having a cyclohexyl ring and 0-4 methyl groups as the only substituents thereon,

at an alkylating temperature above the freezing point of said acid but below C., whereby an additional substituent derived from and having the same number of carbon atoms as said saturated hydrocarbon becomes attached to the adamantane nucleus;

(B) separating the resulting alkylated adamantane; (C) cracking said alkylated adamantane to sever said additional substituent from the adamantane nucleus; (D) and recovering a product comprising olefin having 6. Process according to claim 4 wherein said n-paraffin is n-pentane and isopentene is recovered.

7. Process according to claim 4 wherein said n-parafiin is n-hexane and isohexene is recovered.

8. Process according to claim 2 wherein said saturated hydrocarbon is isoparafiin.

9. Process according to claim 8 wherein said isoparaffin is singly branched and of the C -C range.

10. Process according to claim 9 wherein said isoparaffin is isobutane and isobutene is recovered.

11. Process according to claim 9 wherein said isoparaffin is isopentane and isopentene is recovered.

12. Process according to claim 2 wherein said saturated hydrocarbon is a C C naphthene.

13. Process according to claim 12 wherein said naphthene is cyclohexane and cyclohexene is recovered.

14. A cyclic process according to claim 1 wherein step (D) involves separately recovering said olefin and C -C adamantane hydrocarbon and wherein the recovered C C adamantane hydrocarbon is recycled to step (A).

A cyclic process according to claim 14 wherein said sulfuric acid in step (A) has a strength of at least 96% H 50 wherein used sulfuric acid recovered from step (B) is admixed with S0 in amount to maintain an acid strength of at least 96% H 80 and wherein the resulting mixture is recycled to step (A).

16. In a process wherein a hydrocarbon feed containing olefinic hydrocarbon having at least three carbon atoms per molecule is contacted with a liquid catalyst phase comprising sulfuric acid under conditions causing the formation of aliphatic ester of sulfuric acid, which ester remains in the catalyst phase, and wherein the catalyst activity becomes spent, the method of recovering olefinic hydrocarbon from the spent catalyst phase which comprises:

(A) establishing H SO content in the catalyst phase equivalent to a strength of at least 90% H by weight;

(B) contacting the catalyst phase with adamantane hydrocarbon of the C -C range having 0-3 methyl substituents on the adamantane nucleus at an alkylating temperature in the range of 10100 C., whereby an additional alkyl group derived from said aliphatic ester becomes attached to the adamantane nucleus;

(C) separating the resulting alkylated adamantane;

(D) cracking said alkylated adamantane to sever said additional alkyl group from the adamantane nucleus;

(E) and recovering olefinic hydrocarbon from the cracking reaction product.

PAUL M. COUGHLAN, JR., Primary Examiner V. OKEEFE, Assistant Examiner US. Cl. X.R. 260666 M, 683 R 

